1. Field of the Invention
The present invention relates to a zoom lens system suitable for a single-lens-reflex (SLR) camera using a silver-halide film or a solid-state imaging device and in particular to an internal-focusing zoom lens system capable of focusing by moving a portion of the optical system in a first lens group and also in particular to a compact zoom lens system having a vibration reduction function with a zoom ratio of about four and an angle of view of about 22° or more in a wide-angle end state.
2. Related Background Art
As a conventional focusing method for a zoom lens, a front-lens-group focusing carrying out by moving the most object side lens group to the object has been generally known. This method has a merit that the moving amount for focusing is determined in accordance with the object distance regardless of the zooming position, so that it is effective for simplifying the focusing mechanism. This method makes it possible to construct a first lens group with about three lens elements, so that it is effective for simplifying the construction of the lens system and lowering the manufacturing cost. However, since the moving lens group for focusing is exposed outside, when unexpected force is applied to the lens system, the focusing mechanism, in particular an auto-focusing mechanism, may be damaged. On the other hand, zoom lens systems with an internal focusing method, in which focusing is carried out by a lens group other than the first lens group, have been proposed in large numbers. However, it also has a problem that the moving amount for focusing largely varies in accordance with the zoom position.
In order to solve the problems, a focusing method, in which the first lens group is composed of a front lens group having positive refractive power and a rear lens group having positive refractive power and focusing is carried out by moving the rear lens group to the object, has been proposed in Japanese Patent Application Laid-Open Nos. 6-51202, 2000-19398, and 2000-284174.
However, although each example disclosed by Japanese Patent Application Laid-Open No. 6-51202 constructing the first lens group by three lens elements as a whole, two lens elements in the front lens group and one lens element in the rear lens group, is suitable for simplifying the construction and lowering the manufacturing cost, since focusing is carried out by moving only a single lens element with positive refractive power, spherical aberration, on-axis chromatic aberration and lateral chromatic aberration becomes large upon focusing a close-range object, so that it is undesirable for obtaining high optical performance.
Moreover, each example disclosed by Japanese Patent Application Laid-Open No. 2000-19398 requires five lens elements in the first lens group, three lens elements in the front lens group and two lens elements in the rear lens group, so that it is not suitable for simplifying the construction or lowering the manufacturing cost.
Furthermore, each example disclosed by Japanese Patent Application Laid-Open No. 2000-284174 requires four lens elements in the first lens group, one lens element in the front lens group and three lens elements in the rear lens group, so that it is not suitable for simplifying the construction or lowering the manufacturing cost.
Moreover, telephoto zoom lenses with a vibration reduction mechanism having a zoom ratio of about four have been proposed in Japanese Patent Application Laid-Open Nos. 8-62541 and 10-133114.
Examples disclosed in Japanese Patent Application Laid-Open No. 8-62541 are a five-group zoom lens with positive-negative-positeve-positeve-negative power arrangement or a six-group zoom lens with positive-negative-positive-negative-positive-negative power arrangement moving the second lens group having negative refractive power for vibration reduction. However, in these disclosures, since the effective diameter of the second lens group is 25 mm or more, the vibration reduction mechanism becomes large, so that it becomes difficult to make the zoom lens system be compact.
Examples disclosed in Japanese Patent Application Laid-Open No. 10-133114 are a five-group zoom lens with positive-negative-negateve-positeve-negative power arrangement moving a portion of lens group in the fourth lens group having positive refractive power for vibration reduction. However, in these disclosures, since the effective diameter of the vibration reduction lens group in the fourth lens group is 25 mm or more, the vibration reduction mechanism becomes large, so that it becomes difficult to make the zoom lens system be compact.